BALANUS SULCATINUS (?) _Nyst_, apud D'Omalius (sine descript. aut
tabulâ), Geologie de Belgique, 1853.[100]
[100] I am indebted to M. Bosquet for a specimen, bearing this
name and reference, found in the 'Systeme Bolderien' of Dumont,
(miocene according to Sir C. Lyell) at Bolderberg. The specimen
consists of a rostrum, with a portion of the base attached; and as
these parts are in some degree characteristic, I fully believe this
specimen to be the _B. bisulcatus_. I hope hereafter to give in
the Palæontographical Series fuller illustrations of this and the
following fossil species.
_Radii with their upper margins oblique and smooth; sutural edges
smooth: basis permeated by large pores. Scutum narrow, with from two to
four longitudinal furrows: tergum with the spur very short, broad as
half the valve._
_Var._ plicatus, _with the walls deeply folded; radii narrow, with
their upper margins very oblique_.
_Fossil_ in Coralline Crag, Ramsholt, Gedgrave, Sutton; Mus. S. Wood,
Bowerbank, J. de C. Sowerby. Rauville, dans le Cotentin, Mus. G.
B. Sowerby. _Var. plicatus_, Coralline Crag, Sutton, Mus. S. Wood.
Bolderberg, near Hasselt, Belgium, Mus. Bosquet.
_General Appearance._--Shell conical or tubulo-conical, often rather
globose; walls frequently thin, either very smooth, or deeply
plicated longitudinally: occasionally the same specimen is smooth
in the upper part, and strongly plicated in the lower. The Radii in
the larger specimens are wide, and with their upper margins only
slightly oblique; in the smaller, they are narrower and much more
oblique, but in each case their upper margins are smooth and slightly
bowed. Colour apparently originally nearly white, but with the alæ
generally, in the smaller specimens, clouded with a dark tint:
the radii are usually striped feebly in longitudinal lines. Basal
diameter of largest specimen .8 of an inch; but this seems to have
been an unusual size.
_Scuta_: narrow, with the basal margin forming an unusually small
angle with the occludent margin; surface slightly convex, with lines
of growth approximate, moderately prominent; on the tergal half
of the valve, two distinct rather broad furrows, with sometimes a
third, and even a fourth, nearer to the occludent margin (Pl. 8,
fig. 6 _a_), extend from the apex down the valve, and give it a very
peculiar appearance: the furrows near the tergal margin are the
deepest. Internally, the upper part of the valve is roughened with
small points: the articular furrow is unusually wide: the articular
ridge is very prominent and but little reflexed, with the lower end
almost abruptly cut off: the adductor ridge is prominent, but short:
there are small deepish pits for the rostral and lateral depressores.
_Terga_ (6 _b_), broad, flat, with a slight narrow prominent rim
along the scutal margin, which margin is slightly bowed. The basal
margin on the carinal side of the spur slopes so gradually towards
the spur, that the latter is barely distinct, and is very short, not
depending nearly half its own width beneath the basi-scutal angle: it
is broad, namely, measured across the upper part, as broad as half
the valve; its basal end is obliquely rounded off on the carinal
side; it is placed close to the basi-scutal angle. The carinal
margin of the valve is just perceptibly bowed, and is formed by
rectangularly upturned lines of growth. Internally, the upper part of
the valve is rough; the articular ridge is prominent; the crests for
the tergal depressor muscles are moderately well-developed.
_Parietes_, not porose; internally, the ribs are smooth, with their
basal edges very finely or barely denticulated. The _radii_ (as
already stated) are of variable breadth; they have their upper
margins either very slightly or highly oblique, but always smooth and
rounded: their sutural edges are quite smooth, or sometimes, with
a strong lens, traces of transverse striæ, representing septa, can
just be discovered. The _alæ_ have their upper margins very oblique;
their sutural edges are, in the large specimens, quite smooth; in the
younger ones, plainly crenated; the recipient furrow being clearly
marked with these teeth. _Basis_ plainly porose.
_Varieties._--It is certain that there are longitudinally plicated
specimens of this species, and that the obliquity of the upper
margins of the radii also varies a little: nevertheless some of the
deeply plicated specimens undoubtedly have a very different aspect
from the ordinary varieties, and do really differ in the sutural
edges of the alæ being crenated, and in the greater narrowness and
obliquity of the radii; but these points are all commonly variable.
I have not seen any large specimens of the variety, _plicatus_, so
as to compare them with the large specimens of the normal form, yet
I can hardly entertain any doubt, considering their agreement in
so many important points, that I have rightly treated these forms
as mere varieties; it is unfortunate that none of the specimens of
the _var. plicatus_ seen by me have had opercular valves, as their
presence would have removed all shadow of doubt.
_Affinities_: this is a strongly characterised species, and nearly
allied only to the following species, _B. dolosus_. The furrows on
the scuta in some degree resemble those on _B. lævis_, but there is
no alliance with that species. It is certain that amongst recent
species, the chief affinity is with _B. Hameri_ and _amaryllis_.